The invention relates to making fiber preforms for fabricating parts out of carbon/carbon (C/C) composite material, i.e., having carbon fiber reinforcement and a matrix that is made mainly out of carbon.
One field of application of the invention is that of friction parts made of C/C composite material, and more particularly, disks for airplane brakes.
In order to improve the wear resistance of brake disks made of C/C composite material, U.S. Pat. No. 6,376,431 contemplates incorporating a ceramic, and more particularly, silicon carbide (SiC), within the carbon fiber reinforcement. To this end, the reinforcement or preform is impregnated with a sol-gel type solution containing an SiO2 precursor which serves, after heat treatment, to leave particles of SiC distributed substantially uniformly throughout the preform. The percentage by weight of SiC as introduced in this way is small: not more than 1% of the weight of the composite material.
That known method requires preforms to be manipulated after they have been prepared. The manipulation may be performed in a plurality of stages (before and after impregnation) which are lengthy and expensive and need to be performed with care in order to avoid deforming the impregnated preform (which is then both heavy and soft). In addition, it is not possible to vary in a controlled manner the concentration of SiC particles within the preform. The Applicant has also observed that the presence of SiC particles can affect the mechanical properties of the composite material by weakening the carbon fibers constituting the reinforcement. It is particularly important to retain good mechanical properties in those portions of brake disks that are subjected to mechanical stress, such as the cores of disks that transmit braking torque, and in particular, in aircraft brakes where very high levels of torque need to be transmitted. No weakening of the cores of brake disks can be accepted.
An object of the invention is to enable ceramic particles to be incorporated in fiber preforms for composite material parts while avoiding the above-mentioned drawbacks.